Pregnant Fish

I Have 2 goldfish 1 male an 1 female, recently i noticed that my females smomach is bigger and quite lumpy, i am assuming that she maybe pregnant as i rang the pet shop an asked for advice on her behaviour etc, and he said it sounds like she is, anyway for the last few days i have noticed that the male fish is following the female around the tank, very closely and sometimes looks rather aggressive, i have just left them as the pet shop man said this is quite normal as the male tries to force the female to drop her eggs etc....when i returned to check on them a few hours later i discovered that the tank had gone all cloudy and i cud hardly see anything, i have tried to have a good look for eggs or signs of anything and never spotted anything, what could of caused this? and how long are fish pregnant for? any other advice would be greatly appreciated.
Thanks!!